In lighting arrangements, several light sources can be used together, such as a red and a white light emitting diode, abbreviated LED. A use of three light emitting diodes, a red, a green, and a blue light emitting diode, is also often encountered for RGB lighting. Such lighting arrangements are used, for example, as backlighting for a liquid crystal display.
In order to test whether such a lighting arrangement outputs light with a given wavelength characteristic, lighting arrangements typically provide several photodetectors, which each have different filters. In this way, the light of a red LED is measured by means of a photodetector, which is covered with a filter layer that is transparent for red light. Photodetectors covered with corresponding filters are also provided for a green and a blue LED. This allows white balance correction.